1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to address assignment in a ZigBee network device belonging to a ZigBee network environment, and, more specifically, to a ZigBee network device for separately determining a network parameter under a ZigBee network environment, and an address assignment method of the ZigBee network device.
2. Description of the Related Art
ZigBee features low power consumption and low cost at half the cost of Bluetooth owing to the compactness of its software and related components. ZigBee is a wireless communication technique based on controls and sensors which is suitable for a home network.
The ZigBee network standard specification v0.85[1] defines a cluster tree structure covering all devices in a personal area network (PAN). Every device joining the cluster tree structure is assigned an address according to the tree structure. The assigned address is used for the routing in the ZigBee network environment.
For the address assignment, a ZigBee coordinator defines two network parameters Cm and Lm in consideration of the size of the entire network. Cm is a maximum number of devices connectable to each device (hereinafter, referred to as children), and Lm is a maximum level depth of the tree structure.
According to a conventional address assignment method in the ZigBee network environment, an address is assigned to each device. The ZigBee coordinator assigns addresses taking into account that the children of each device are connected to each device. For example, the ZigBee coordinator with the address s assigns s+1 to a first device. A second device is assigned s+1+CskipLs. The address of Cm-th device is s+1+(Cm−1)·CskipLs. CskipLs can be obtained from Equation 1.
                              Cskip          Ls                =                                            B              L                        -                                          ∑                                  k                  =                  0                                Ls                            ⁢                                                          ⁢                                                (                  Cm                  )                                k                                                          Cm                          Ls              +              1                                                          [                  Equation          ⁢                                          ⁢          1                ]            
In Equation 1, BL is an address size of the whole network, and Ls is a level number of the ZigBee coordinator with the address s. BL can be derived from Cm and Lm based on Equation 2.
                              B          L                =                              1            -                          Cm                              Lm                +                1                                                          1            -            Cm                                              [                  Equation          ⁢                                          ⁢          2                ]            
The ZigBee coordinator provides the defined Cm and Lm to each device. Each device assigns addresses to its respective children in the same manner.
FIG. 1 is a conceptual diagram of the conventional ZigBee network environment where the addresses are allocated according to the conventional method. In FIG. 1, a device A serves as a top ZigBee coordinator. The address of the device A is 0, and Cm and Lm are determined to be 4, respectively. Devices B, C, and D are connected to the Device A as its children. The whole address size BL assignable by the top ZigBee coordinator is 341 based on Equation 2. CskipLs, of the top ZigBee coordinator is 85 based on BL and Equation 1. Thus, the interval between the addresses of the children B, C, and D is 85. Specifically, the address of the first device B is 1, the address of the second device C is 86, and the address of the device D is 171. Cskip of the device B, C, and D at the first level (Ls=1) is 21 based on Equation 2. Thus, addresses of devices E though J at the second level (Ls) are at 21 intervals.
According to the conventional method as illustrated in FIG. 1, each device assigns the addresses using the fixed Cm and Lm over the while ZigBee network. The devices receive Cm and Lm from their parents and assign the addresses to their children based on Equation 1 and Equation 2.
An end-device to which children cannot be connected, may be connected to the mid-level of the ZigBee cluster tree. If the address is assigned to the end device in the manner discussed above, the address resources are wasted: For example, if a device E is an end-device, the address block {3˜28} cannot be used by any device since these addresses are reserved for device E's descendants. As a result, the addresses are wasted and cannot be used efficiently.
In this regard, a new parameter Rm, which indicates the maximum number of children of each device with routing ability, is defined and used for the address assignment. CskipLs can be changed to Equation 3.
                              Cskip          Ls                =                              1            +                          C              m                        -                          R              m                        -                                          C                m                            ·                              R                m                                                      L                    m                                    -                                      L                    s                                    -                  1                                                                          1            -                          R              m                                                          [                  Equation          ⁢                                          ⁢          3                ]            
As for a device with the routing ability and operable as the coordinator with respect to other devices, an address space is reserved in consideration of its descendents. In contrast, the continuous addresses are assigned to the end-device.
FIG. 2 is a conceptual diagram illustrating conventional ZigBee address assignment. In FIG. 2, Rm=2, Cm=4, and Lm=3. Since Rm=2, the top ZigBee coordinator A can have two devices B and C with the routing ability and two devices D and E without the routing ability. Address blocks {1˜13} and {14˜26} are assigned to the devices B and C, respectively. Meanwhile, the continuous addresses 27 and 28 are assigned to the devices D and E, respectively. The above address assignment can avoid the waste of the address space. However, Cm and Lm are fixed to all of the devices with the routing capable devices according to the conventional method as shown in FIG. 2. As the devices have different characteristics and different conditions, the number of the children also varies. Therefore, the waste of the address space is inevitable due to the fixed Cm and Lm.